Production of alkaline earth metals



Patented Nov. 14, 1939 UNITED STATES PATENT OFFICE No Drawing.Application December 30; 1938, Serial No. 248,521

11 Claims.

This invention relates to a method and com position for use in theproduction of alkaline earth metals.

Alkaline earth metals may be produced-conventionally by electric furnaceheating of a reducing agent with a material bearing the oxide of themetal, carbon being an example of the reducing agent.

Aluminum powder also may be used as the reducing agent. Its use,however, introduces a difficulty. Being combustible, and in extremelyfinely divided form; the powder is hazardous from the explosionstandpoint. Being dusty, it is entrained with the alkaline earth metalvapor, so as to contaminate the metal produced. In addition, there isalso waste of the aluminum powder; the loss of powder carried with thevapor makes impossible accurate calculation of amounts of theingredients to be used in a charge, particularly since the amount ofpowder lost varies with the rate of release of the alkaline earth metalvapor, which, due to irregularities in furnace operation, cannot alwaysbe maintained at a uniform rate.

It is an object of the invention to provide a method in which desiredintimacy of contact of aluminum with the selected oxide bearing materialmay be obtained, without the need of using aluminum powder. Anotherobject is to avoid dust contamination of the distilled alkaline earthmetal. Other objects and advantages of the invention will appear fromthe description which follows.

Briefly stated, the invention comprises the production of an alkalineearth metal by heating a material bearing its oxide with aluminum foil.The invention comprises also special means of obtaining very intimateassociation of the said material with aluminum supplied in the form offoil.

The invention will be illustrated more particularly by reference 'to themanufacture of magnesium.

The process and equipment used are conventional, except as noted herein.Thus, magnesium oxide or a source thereof and admixed aluminum areheated in the absence of air, to avoid oxidation of the metal produced,in a usual type of furnace including electrical heating elements, an

5 or the like. The vapors are passed through an outlet from the furnacefor the magnesium vapor outlet and delivery pipe, advantageouslyresembling somewhat a tuyere in the side of the furnace, at a positionabove the level of the charge therein, and thus delivered to a condenserof typecominonly used in the manufacture of mag- I nesium.

The condensed magnesium may be obtained in finely divided or compactor'masslve form, say, as a powder, liquid or solid, the condensation andcoilection of the magnesium being made in an atmosphere of hydrogen orother suitable .inert or reducing gas.

A departure is made from the usual practice in that the aluminum, forreducing the magnesium oxide containing compound to the metallic orelemental condition, is foil. Preferably the aluminum foil used is thin,say, about 0.0025 to 0.0002 inch in thickness. Scrap material from thewrapping of confectionery, food products, cigars, cigarettes, or chewinggum, is satisfactory. 20 The heat-insulating grade of aluminum foil,either by itself or backed with paper may be used.

As the magnesium oxide bearing material,

there is preferred a relatively high grade magnesium oxide, such as thatnow being manufactured by the wet process and utilized in the commercialproduction of magnesium compounds. Also there may be used calcinedmagnesite, (1010- 30 mite or brucite.

The aluminum foil and the selected source of magnesia are mixedintimately, as in a wheel or pan mill or in other suitable manner. Forthe sake of economy in the use of the aluminum foil, I prefer to use themagnesium oxide bearing material in amount somewhat in excess of thealuminum foil as. calculated from the equivalent weights of the twomaterials. The foil may also be shredded preparatory to making up thecharge 40 of magnesium oxide and aluminum foil.

The charge in unbriquetted condition is heated, as, for instance, in afurnace of the kind described, to a temperature at or above the meltingpoint of aluminum. As the foil softens, it tends, 5 under the largeforce of its surface tension, to contract into spheres. But it isrestrained from doing so by the presence of contacting particles ofmagnesium oxide. As a result, the foil is drawn into or it surface-wets.the said particles. 5

The temperature of the mixture is then raised to that of volatilizat-ionof the resulting magnesium, so that magnesium in the form of vaporpasses from the furnace to the condensing system. There is practicallyno aluminum carried over as dust or as finely divided liquid mist in thedistillation of the magnesium.

' Since the boiling point of magnesium is about 1,100 C., thetemperature of heating is preferably at least 1,110 C. or somewhathigher. It

is kept well below the boiling point of aluminum but at a temperaturesufiiciently high to cause volatilization of liberated magnesium.

To obtain a still more intimate association of 19 the aluminum with themagnesium oxide bearing material, the charge to be used in theproduction of magnesium may be evacuated, to withdraw a large part orpractically all of the gas therefrom. This evacuation may be made ifdesired in a suitable pretreating vessel that is practically air tight.Evacuation may be made either before, during or after the heating of thecharge, but the charge in any case should be above the melting point ofaluminum when the vacuum is .0 broken. I

When the aluminum foil has melted, the vacuum is broken by the admissionof 'inert (nonoxidizing) gas such as hydrogen, helium or methane. Theresulting increase of pressure forces molten aluminum into the evacuatedpores or spaces within the finely divided magnesium oxide bearingmaterial, with resultant and very satisfactory association of thecomponents of the mixture. In other words, the aluminum and the gomagnesium oxide bearing material are brought into intimate contact by aprocess of surface wetting of the oxide by molten aluminum, under theinfluence of vacuum and pressure successively applied. As a result thereis impregna- 'tion of the molten aluminum into the magnesium oxidebearing material. An advantage of this wetting and impregnating is thatthe method can be applied to relatively coarse or granular material,which can be fed into a smelting furnace and reduced so as greatly tominimize the phenomenon of dusting and permit greater speed of reactionand ease of escape of the metallic vapor from the charge. when theevacuation process is used even aluminumpowder may be used withoutexcessive dusting.

Whether the evacuation and subsequent admission of the inert'gas hasbeen efiected in an outside vessel or in the smelting furnace itself,the mixture is now heated in the furnace to distil magnesium therefrom.

The production of magnesium as described avoids the difliculty ofexcessive contamination of the distillate by aluminum carried over infinely divided condition. Also, the process is one that may be performedsimply and economically, and with an improvement in the quality of thecondensed product.

In place of the magnesium oxide bearing material used in the examplesabove, there may be substituted an equivalent amount of a materialcontaining barium oxide, strontium oxide, or calcium oxide. When suchsubstitution is made, the process used to produce the alkaline earthmetal is the same as described, final heating in all cases beingeffected at a temperature somewhat above the boiling point of the metalwhose oxidic material has been selected.

Among the materials that may be substituted for the magnesium oxide orthe like are the carbonates of barium, strontium and calcium, preferablyin calcined condition, or any materials that give under smeltingconditions the oxide of the alkaline earth metal that is to be produced.Aluminum foil backed with paper, cotton fabric or other cellulosicmaterial may be substituted In a modification of the method using thetoil with cellulosic backing, the temperature of smelting is raised tothat at which the carbon becomes effective.

In that case, the distilled metal vapor is subjected to shockcondensation in well known manner, to prevent a reverse reaction betweenthe liberated metal and the carbon monoxide produced from the carbon asreducing agent for the metal oxide.

It will be understood that the term bearing" or containing" as appliedto the oxide is used herein to include oxide providing or supplying,under the smelting conditions and at the furnace temperatures recited.

It will be understood, also, that the details given are for the purposeof illustration, not restriction, and that variations within the spirltof the invention are intended to be included in the scope of theappended claims.

I claim:

1. The process of producing an alkaline earth metal which comprisesforming a mixture of aluminum foil and a material bearing an oxide ofthe alkaline earth metal, heating the mixture in unbriquetted conditionin a furnace in the absence of air to a temperature at least as high asthat of volatilization of the alkaline earth metal and below the boilingpoint of aluminum, passing the volatilized metal from the furnace, andthen condensing the vapor.

2. The process of producing an alkaline earth metal which comprisesforming a mixture of aluminum foil and a finely divided oxide of analkaline earth metal, heating the mixture in unbriquetted condition in afurnace in the absence of air to a temperature at least as high as thatof volatilization of the alkaline earth metal and below the boilingpoint of aluminum, passing the volatilized metal from the furnace, andthen condensing the vapors.

3. The process of producing magnesium which comprises forming anintimate mixture of aluminum foil and a finely divided magnesium oxidebearing material, heating the mixture in unbriquetted condition in afurnace in the absence of air to a temperature at least as high as thatof volatilization of magnesium and below the boiling point of aluminum,passing the volatilized magnesium from the furnace and then condensingthe vapors.

4. The process of producing an alkaline earth metal which comprisesforming a mixture or aluminum foil of thickness of the order of 0.0025to6.0002 inch and a finely divided material bearing an oxide of thealkaline earth metal, heating the mixture in unbriquetted condition in afurnace in the absence of air to a temperature at least as high as thatof volatilization of the alkaline earth metal, passing the volatilizedmetal from the furnace, and then condensing the vapors.

5. The process of producing an alkaline earth metal which comprisesforming a mixture of aluminum and a finely divided material bearing anoxide of the alkaline earth metal, heating the mixture to a temperatureabove the melting point of the aluminum and below the boiling point ofthe alkaline earth metal, evacuating the heated mixture, admitting aninert gas to the evacuated mixture, so as to force molten aluminum intointimate association with the said material, and then heating themixture to the temperature of volatilization of the alkaline earth metaland distilling the said metal.

6. The process of producing an alkaline earth metal which comprisesforming an intimate mixture of aluminum and a material bearing an oxideof the alkaline earth metal, heating the mixture in an inert atmosphereto a temperature above the melting point of the aluminum and below theboiling point of the alkaline earth metal, evacuating the mixture,admitting an inert gas to the evacuated mixture subsequent to themelting of the aluminum, so as to force molten aluminum into intimateassociation with the said material, and then heating the mixture to thetemperature of volatilization of the said metal and distilling themetal.

7. The process of producing magnesium which comprises forming anintimate mixture of aluminum foil and a finely divided magnesium oxidebearing material, evacuating the mixture, heating the evacuated mixtureto a temperature above the melting point of the aluminum foil and belowthe boiling point of the magnesium, admitting an inert gas to theevacuated and heated mixture, so as to force molten aluminum intointimate association with the said material, and then heating themixture to the temperature of volatilization of magnesium and distillingthe resulting magnesium.

8. The process of producing magnesium which comprises forming anintimate mixture of finely divided aluminum with a finely dividedmagnesium oxide bearing material, heating the mixture in an inertatmosphere to a temperature above the melting point of the aluminum andbelow the boiling point of magnesium, evacuating o the heated mixture,admitting an inert gas to the evacuated mixture so as to force moltenaluminum into intimate association with thesaid material, and thenheating the mixture to the temperature of volatilization of magnesiumand distilling the resulting magnesium.

9. The process of producing an alkaline earth metal which comprisesforming a mixture of aluminum foil having a cellulosic backing and amaterial bearing an oxide of the alkaline earth metal, heating themixture in a furnace in the absence of air to a temperature at least ashigh as that of volatilization of the alkaline earth metal and below thetemperature of reduction of the alkaline earth metal oxide by carbon,passing the volatilized metal from the furnace, and then condensing thevapor.

10. The process of producing an alkaline earth metal which comprisesforming an intimate mixture of aluminum and a material bearing an oxideof the alkaline earth metal, evacuating the mixture, admitting to theevacuated mixture 9. gas that is inert to aluminum and magnesium,heating the mixture in an atmosphere of the inert gas to the temperatureof volatilization of the alkaline earth metal but below the boilingpoint of aluminum, separating the resulting vapor 'of the alkaline earthmetal from the said mixture, and then condensing the vapor.

11. The process of producing an alkaline earth metal which comprisesforming a mixture of amminum foil having a charred cellulosic backingand a material bearing an oxide of the alkaline earth metal, heating themixture in a furnace in the absence of air to a temperatureat least ashigh as that of volatilization of the alkaline earth metal and below thetemperature oi reduction of the alkaline earth metal oxide by carbon,passing the volatilized metal from the furnace, and then condensing thevapor.

FRANK R. KEMMER.

